1. Field of the Invention
The present invention relates to the radiographic technology, and more particularly to an imaging system using a straight-line trajectory scan to improve the speed of a radiographic security inspection.
2. Description of the Prior Art
Security inspection is much more significant in anti-terrorism and anti-drug-smuggles. After 911, US makes more and more account of the security inspection in public places such as airports and railway stations. In addition, with the development of anti-drug-smuggles, the requirements for inspecting containers and luggage at Custom are increased.
Current security inspection systems are mainly radiographic systems, and in the radiography field, radioscopic system such as DR (digital radiography) is commonly used, while stereo-imaging equipment such as CT (computed tomography) system is not widely employed. This is because a practical security inspection system generally performs an on-line real-time inspection and thus a fast scanning and imaging speed of the inspection system is required. For example, for civil aviation luggage inspection, a custom clearance rate of 0.5 m/s is required. However, this requirement can hardly be satisfied currently even if a spiral CT with a large pitch is employed. Further more, in regard to some large objects such as custom containers, it is very difficult to rotate the containers or the radiation source and the detectors. Besides, the cost of devices for the CT system is quite high. These above and other factors prevent the CT system from being widely used in the security inspection field. However, compared with the CT systems, a radioscopic system has a drawback of no ability of avoiding an overlapping effect of objects in a radiation direction, and thus the inspection capability is restrained so that a real stereoscopic inspection and location can not be performed well.
With the development of CT techniques, a tomographic image having a certain quality can be reconstructed in a case of situation where a limited angle projection data is obtained or the data is truncated. Thus, it becomes practical to apply an incompletely scan and reconstruct an approximate images. Theoretically, for an imaging system with a straight-line trajectory, if the length of scanning trajectory is infinite, an exact reconstruction could be achieved. If the trajectory is of a finite length, then it is equivalent to a limited-angle CT scan. Therefore, by using CT reconstructions dealing with incomplete data, cross-section images can be obtained from a straight-line imaging system, and the stereoscopic radiography is achieved.
An imaging system with a straight-line trajectory, Computed Laminography system, has already been proposed. However, it has a small range of the source coverage and reconstruction algorithms for tomosynthesis are used, which results in a poor capability of three-dimension imaging. Consequently, an imaging system capable of speedily achieving the three-dimension imaging and tomographic images is required.